Well drilling method

ABSTRACT

A well drilling fluid comprises a solution having dissolved therein a relatively small quantity of potassium silicate or, for some applications, sodium silicate or a mixture of sodium silicate and potassium chloride. The body of the fluid may be water or a presently available mud or other drilling fluid with which the silicate is compatible. The fluid on reaching shale sections along the well bore acts to stabilize the shale and prevent its swelling, dispersing or sloughing.

United States Patent Hill [ 51 July 25,1972

[54] WELL DRILLING METHOD [72] Inventor: Gilman A. Hill, 6200 PlateauDrive,

Littleton, Colo. 80120 [22] Filed: March 2, 1970 [21] Appl. No.: 15,850

[52] US. Cl ..166/292, 175/46, 175/66, 175/71, 252/85 B [51] lnt.Cl.....E2lb 21/04, E2lb 33/138 [58] Field of Search ..252/8.5 A, 8.5 B, 8.5P;

[56] References Cited UNITED STATES PATENTS 2,146,693 2/1939 Vietti eta1 ..252/8.5 B 2,165,824 7/1939 Vietti et al.....

2,353,230 7/1944 Garrison et al. 252/8.5 B 3,244,230 4/1966 Sharp166/292 2,402,588 6/1946 Andresen.... ..166/270 2,452,021 10/1948 Wayne..252/8.5 A

2,165,823 7/1939 Vietti et a1 ..252/8.5 B

2,205,609 6/1940 Vail et a]. ...252/8.5 B

3,318,396 5/1967 Tailleur "252/85 B OTHER PUBLICATlONS Rogers,Composition and Properties of Oil Well Drilling Fluids" 1st Edition,Gulf Pub. Co., Houston, Tex. 1948, pp. 417 to 427.

Primary Examiner-Stephen J. Novosad Attorney-McGn-ew and Edwards [57] 7ABSTRACT 3 Claims, No Drawings WELL DRILLING METHOD My invention relatesto fluids employed in the drilling of oil and gas wells and the like andparticularly to an improved well drilling fluid for decreasing orpreventing problems arising from the swelling, dispersing or sloughingof shale sections in the well bore.

During the drilling of oil and gas wells severe problems have beenencountered due to the swelling, dispersing and caving or sloughing ofshale sections at the wall of the well bore. It is desirable to avoid oreliminate such problems and, accordingly, it is an object of thisinvention to provide an improved method for drilling well bores andminimizing the swelling, dispersing, sloughing or caving of shalesections at the wall of the well bore.

It is another object of this invention to provide an improved welldrilling fluid for well bores which pass through shale sec- -tions.

Briefly, in carrying out the objects of my invention in one embodimentthereof, I prepare a drilling fluid which includes a relatively smallquantity of potassium silicate dissolved therein. When drill a wellemploying the method of this invention there is added to the well fluidand dissolved therein a quantity of potassium silicate. Anotherembodiment of my invention, for some applications, employs sodiumsilicate instead of potassium silicate. In still another embodiment ofmy invention, for some applications, I use a mixture of sodium silicateand potassium chloride.

The features of novelty which characterize this invention are pointedout with particularity in the claims annexed to and forming a part ofthis specification. The invention itself, however, both as to its methodof drilling and the composition of the fluid, together with furtherobjects and advantages thereof, will best be understood upon referenceto the following description.

Well drilling fluids vary widely in composition and density dependingupon the nature of the geologic formations through which the wells areto be drilled. The drilling fluid may be either water based or oil basedcontaining water and may contain various materials and additives whichprovide a so-called drilling mud". When these fluids encounter certainshales in the walls of the bore, the reaction of the drilling mud on theshale frequently results in the swelling, dispersing and sloughing ofportions of the shale section which may result in substantial caving orcollapse of the hole. I have discovered that by providing a smallquantity of potassium silicate or of sodium silicate in the drillingfluid that the sloughing and caving of a shale wall section may beminimized or prevented. The quantity of the silicate may vary over awide range. In many cases, the concentration of the silicate by weightpercent may range from 1 to 2 percent of the drilling mud solution. Insome cases, concentration as dilute as one-fourth to one-half percentmay be adequate, and in other cases concentrations of 3 to 4 percent ormore may be necessary to control the reaction of the shales. Whiledrilling, samples of the drill cuttings brought to the surface with thedrilling mud can be tested in varying concentrations of potassiumsilicate, sodium silicate or mixtures of sodium silicate with potassiumchloride. From the results of such testing of the drill cuttings, the optimum composition and concentration of the solution may be determined.Also, it is necessary to restrict from use in the drilling mud anyconstituents which may be incompatible with the silicate solutions.

From the standpoint of economy, I have found that commercially availablepotassium silicates are well suited to my process and for my drillingfluid and are available in bulk quantities at prices making their use inthe practice of this invention entirely feasible. Sodium silicate may beobtained at a lower price and may be preferable for some applicationsfor this reason. In some applications it may be economically preferableto use a combination of sodium silicate with potassium chloridesalt toachieve the combined favorable effects of both the potassium ions andthe ionized silicate chain complexes.

In practicing the invention, the well drilling fluid may be made upinitially with the desired percentage solution of silicate or for someapplications it may be desirable to add the silicate only when shalesections are encountered. During the drilling of a well bore thedrilling fluid is circulated and returned to a tank, pit, sump or supplyreservoir. This supply fluid may be checked periodically to maintain thedesired percentage of silicate in solution and additional quantities ofthe silicate may be introduced if strengthening of the solution isdesirable.

The temperatures in well bores increase with depth and at depths belowabout four thousand feet are generally in excess of F. In thistemperature range, the reaction of the salts and the shale iseffectively rapid. For shallower wells where the temperatures are lowerit may be desirable to heat the drilling fluid to bring it up to atemperature in the more effective range in order to accelerate the shalestabilizing action.

In some drilling operations, it may be desirable to operate the drillfor a selected period of time using a fluid with none of the silicateadded or with a low concentration and then after stopping the operationcirculating to the bottom of the hole drilling fluid with a normal orhigh concentration of the silicate and allowing this to remain incontact with the bore wall for a substantial time. By operating in thismanner, it will be understood that the shale cuttings present in thefluid during drilling will use up little or none of the silicatesolution and that the silicate treatment at full strength will beapplied to the bore wall after the drilling has stopped and the majorityof the drill cuttings have been removed from the bore. By way ofexample, drilling may be continued over a predetermined period, saytwelve hours, using no silicate or a low concentration and then thedrilling operation temporarily suspended and the full strength silicatesolution may be circulated to the bottom of the hole for treatment ofthe zone just drilled. in particular, it may be advantageous tocirculate to the bottom of the hole the concentrated solution beforewithdrawing the drill string so the full strength treatment may beeffected throughout a selected length of the bore while the string iswithdrawn for replacement of the drill bit. This periodic treatmentprocedure results in substantial saving of the silicate solution.

I claim:

1. The method of drilling a well bore through a geologic formationincluding a shale section and preventing significant swelling,dispersing and sloughing of the shale which comprises providing a watercontaining drilling fluid and dissolving therein a quantity of solublesalt from the group consisting of potassium silicate and sodium silicateand a mixture of sodium silicate and potassium chloride, the fluidemployed during active drilling being maintained with a lowconcentration of the soluble salt and wherein upon cessation of drillingthe concentration is increased in the fluid in the drilled portion ofthe bore for treatment of that portion before resuming drilling.

2. The method of drilling a well bore through a geologic formationincluding a shale section and preventing significant swelling,dispersing and sloughing of the shale which comprises providing a watercontaining drilling fluid and dissolving therein a quantity of solublesalt from the group consisting of potassium silicate and sodium silicateand a mixture of sodium silicate and potassium chloride, theconcentration of soluble salt in the drilling fluid being maintained lowduring drilling and increased in the fluid circulated to the bottom ofthe bore upon cessation of drilling for treatment of the freshly drilledportion of the bore.

3. The method of drilling a well bore through a geologic formationincluding a shale section and preventing significant swelling,dispersing and sloughing of the shale which comprises providing a watercontaining drilling fluid and dissolving therein a quantity of solublesalt from the group consisting of potassium silicate and sodium silicateand a mixture of sodium silicate and potassium chloride, including thestep of drilling the shale section, testing the cuttings with a range ofthe salt solution and determining the optimum concentration of salt tobe added to the fluid.

2. The method of drilling a well bore through a geologic formationincluding a shale section and preventing significant swelling,dispersing and sloughing of the shale which comprises providing a watercontaining drilling fluid and dissolving therein a quantity of solublesalt from the group consisting of potassium silicate and sodium silicateand a mixture of sodium silicate and potassium chloride, theconcentration of soluble salt in the drilling fluid being maintained lowduring drilling and increased in the fluid circulated to the bottom ofthe bore upon cessation of drilling for treatment of the freshly drilledportion of the bore.
 3. The method of drilling a well bore through ageologic formation including a shale section and preventing significantswelling, dispersing and sloughing of the shale which comprisesproviding a water containing drilling fluid and dissolving therein aquantity of soluble salt from the group consisting of potassium silicateand sodium silicate and a mixture of sodium silicate and potassiumchloride, including the step of drilling the shale section, testing thecuttings with a range of the salt solution and determining the optimumconcentration of salt to be added to the fluid.